It all depends on the wire gauge you use and and length of the wire used to get your selected turns ratio.

There are many ways to combat this ,from wire size to multiple windings in connected in parallel.

The latter being more ideal as this would increase core coverage and reduce the leakage inductance.

For practicablity reason by using multiple windings in parallel, the DCR of transformer should be much less than the ribbon itself, not to mention the DCR of the transmision line feeding the ribbon from the transformer as well.

Most of us don't use garden hoses.
But that is about the right guage!
I would try (DIY) many many layers of aluminium or copper tape that you can find at your local hobby shop or hardware store.
Laminated with an insulating material like polyurethyn or something.jer

I want amorphous cores and good coupling between windings... LF response is of no interest. Since the secondary is few turns, that is why copper foil is used and not just a handful of turns of say 8ga. At least this is what I am told, having not made one myself.

You seem to be understanding okay.
Just remember all of the same rules apply.
the larger the core ,less turns on primary(as per lowest frequency),therefore a lower overall DCR.
one reason for using a flat conductor as a winding is to increase core coverage to lower leakage inductance.
This where I had left off in my study due to equipment failure as I was pushing everything past a pheasible limit.
I had figured out that by just by spreading out the 10 turns of wind reduced the leakage inductance greatly.
And even more so when I used 4 10 turn windings in parallel to get complete coverage.
It was bolsert that told me that if you double the winding coverage you will half the leakage inductance.
I had found this to be true and I had planned to show this when I had burned up my last meter due to the highvoltage rf caused by the crossover distortion of the amp, in combination with the leakage inductance and transformer capacitance causing it to resonate,basicaly forming a tesla coil.
There is some info on using amorphous cores at 6moons.com . jer